I'm sure this very problem has been up for discussion before, but since I really could not find what I was looking for I decided to try it. My iMac gets a kernel panic once in a while. From what I can tell by previous posts on the forum it is because of incompatible memory. I recently purchased Corsair Value DDR3 SO-DIMM 1333MHz 16GB (2x8GB). Originally i wasn't thinking having the old Apple RAM in it, so I would have "just" 16GB. The problem, however, is that my iMac wont boot without the original Apple RAM. It boots with all four RAMs in it, but not with just the two Corsair's. Checking my system info, it says "OK" on all the RAMs with the same speed. I've tried placing the new RAMs in the slots where the old RAMs were placed and in the free slots leaving the two previous occupied slots free. It just freezes on the Apple-logo at startup. There isn't even any loading going on. Any ideas on what I can do? Thanks!